CYCLIC nucleotide-gated (CNG) channels serve as downstream targets of signalling pathways in vertebrate photoreceptor cells and olfactory sensory neurons (see ref. 1 for review). Ca2+ ions that enter through CNG channels(2-5) intimately control these signalling pathways by regulating synthesis(6) or hydrolysis(7) of cyclic nucleotides, and by decreasing ligand sensitivity of CNG channels(8). Several lines of evidence suggest that cyclic nucleotides and Ca2+ play important roles in chemotaxis of invertebrate sperm and fertilization (see ref. 9 for review), whereas their mechanisms of action in vertebrate sperm are largely unknown. Here we report the cloning and functional expression of a novel CNG channel from bovine testis. The channel polypeptide was functionally localized in sperm, but is also specifically expressed in cone photoreceptor cells. These channels might be involved in chemotaxis of sperm by controlling Ca2+ entry through a cyclic-nucleotide signalling pathway.